Musnad Abu Ya'la al-Mawsili 219:8

Abu Khaythama narrated to us, Ya'qub ibn Ibrahim narrated to us, my father narrated to us, from Ibn Ishaq, who said: Abu Ja'far Muhammad ibn 'Ali and Nafi' narrated to me that 'Amr ibn Nafi', the freed slave of 'Umar ibn al-Khattab, narrated to them that he used to write the copies of the Mushaf during the time of the wives of the Prophet, may Allah bless him and grant him peace. He said: Hafsa asked me to write a Mushaf for her and said to me: "When you reach this verse in Surat al-Baqarah, do not write it until you bring it to me, so that I may dictate it to you as I memorized it from the Messenger of Allah, may Allah bless him and grant him peace." He said: When I reached it, I brought her the sheet upon which I was writing. She said: "Write: 'Guard strictly the prayers, especially the middle prayer and the afternoon prayer, and stand before Allah with devotion.'"